1. Field of the Invention
The present invention relates to a transfer printer, such as a label printer for printing item names, bar codes, etc. on labels, and more particularly, to a transfer printer in which a transfer ribbon in contact with printing paper is heated by means of a print head to transfer ink on the ribbon to the paper, thereby effecting printing.
2. Description of the Related Art
A transfer printer, e.g., a label printer for printing item names, bar codes, etc. on labels, comprises a printing section which includes a platen roller and a line thermal head adapted to be pressed against the roller. A supply shaft and a take-up shaft for a transfer ribbon are located over the printing section. When the take-up shaft is rotated by means of a motor and the like, the transfer ribbon is fed out from the supply shaft, transported past a guide shaft and the printing section, and taken up by means of the take-up shaft. The supply shaft is connected with a load mechanism. A desired back tension is applied to the transfer ribbon by damping the rotation of the supply shaft by means of the load mechanism.
Conventionally, attaching and detaching operations for replacing the transfer ribbon, must be performed in a narrow space within the printer body, while avoiding interfering with other components, so that the working efficiency is not very high.
A printer of a novel design has recently been developed to facilitate the replacement of the transfer ribbon. In this printer, a supply shaft and a take-up shaft wound with a ribbon are housed in a casing to form a modular structure or unit, which is removably mounted in the body of the printer. According to this arrangement, the transfer ribbon can be replaced outside the printer by removing the unit from the printer body.
If the prior art transfer ribbon and the supply and take-up shafts are combined into the unit, the replacement of the ribbon itself can be significantly facilitated. Nevertheless, the ribbon unit must be attached to or detached from the printer in the narrow space within the printer body, so that the working efficiency is not satisfactory. Thus, it is hard to utilize the ribbon unit with high efficiency.
In the ribbon unit, both the supply shaft and the take-up shaft include a ribbon set shaft and a cylindrical core removably mounted on the set shaft. The transfer ribbon is wound on the core.
A core fixing portion in the prior art is formed on one end portion of the ribbon set shaft, and a core stopper portion is formed on the other end portion. One end portion of the core is removably fitted on the fixing portion, so that the core is prevented from moving radially and axially toward the one end side with respect to the ribbon set shaft. The stopper portion is releasably engaged with the other end of the core so that the core is held between the stopper portion and the fixing portion, whereby the core is prevented from moving toward the other end of the set shaft. Thus, the core is supported on the ribbon set shaft by means of these two portions, and is rotated together with the set shaft.
The core fixing portion and the core stopper portion, are provided individually at the two opposite ends of the ribbon set shaft; both are immovable, and the distance between these portions is previously set in accordance with the width of the transfer ribbon to be used. In other words, the distance between the two portions is not adjustable.
Currently available transfer ribbons have widths of two, three, four, and six inches. In the conventional printer, however, the ribbon set shaft is adapted to be used exclusively for a specific transfer ribbon, as mentioned above. Accordingly transfer ribbons having widths which conform to the different widths of various printing papers cannot be set on one and the same ribbon set shaft. If a transfer ribbon of 4-inch width is used, for example, part of it can be used for printing on papers of widths smaller than its width. In this case, however, the ribbon is consumed wastefully.
Also in this respect, therefore, the ribbon unit cannot be efficiently utilized.